Thermocurable resin compositions are useful as a mechanical component material, an electrical or electronic component material, an automobile component material, a civil engineering and construction material, a forming material and the like. Further, the thermocurable resin compositions are used as a coating material or a material for adhesives. Further, such thermocurable resin compositions are particularly useful as an electrical or electronic component material or a material in an optical application because they can also exhibit transparency. For example, the size of a digital camera module has been reduced because it is installed on a cellular phone and the like. Further, a reduction in costs on such a module has been needed. Accordingly, a lens made of a plastic material such as polymethyl methacrylate, polycarbonate, and polycycloolefin has been increasingly adopted instead of an inorganic glass, which is commonly used. Recently, as a new application of these plastic materials, needs for in-vehicle applications such as an in-vehicle camera and a bar-code reader for delivery service have been increased. In these applications, long-term heat resistance, that is, heat resistance more excellent than that of the commonly used plastic materials is needed in view of exposure to high temperatures in summer. Hence, the use of the thermocurable materials has been increasingly studied. In addition, a plastic material which endures a solder reflow process has been needed.
With regard to conventional materials used as an electrical or electronic component material or used in an optical application, Japanese Kokai Publication No. 2004-346288 on pages 2 and 13 discloses a method for producing a thermocurable resin composition, in which a thermocurable resin including an alicyclic epoxy resin is dissolved and mixed with an organic solvent in which inorganic particles having a particle size of 70 nm or less have been dispersed, and from this mixture, the organic solvent is removed, and thereto, a curing agent is added and mixed. However, the thermocurable resin composition obtained in such a production method has insufficient transparency and therefore it cannot be used in an optical application and the like. Therefore, it is needed that coarse inorganic particles are completely dispersed to be primary particles in order to prevent the inorganic particles from scattering visible light, and thereby the transparency is increased to a sufficient high level. Further, Japanese Kokai Publication No. 2004-396288 discloses a resin containing an alicyclic epoxy and a dispersion prepared by dispersing dry silica in a solvent. However, such a resin has room for improvement in that flexibility, resistance to fracture, anti-thickening effect, prevention for impurity incorporation at the time of mixing of a beadmill, for example, are appropriately improved, and further optical characteristics such as transparency can be sufficiently improved. In addition, the following is desired if such a resin composition is molded and processed in a mold and the like. The demoldability which is shown when the cured product is demolded is improved, and thereby a molded body is produced with high productivity.
Further, Japanese Kokai Publication No. 2004-250521 on pages 2 and 7 discloses an epoxy resin molded body produced by curing a composition containing at least an epoxy resin and inorganic oxide particles, wherein inorganic oxide particles having an average particle diameter of 50 nm or less are dispersed into the molded body. This discloses an epoxy resin composition containing wet silica and an epoxy resin as an example, and bisphenol A (having an Abbe number of 34.1) is used as the epoxy resin. However, in such a case, there is need to suppress thickening during solvent degassing while a concentration of the silica is maintained to a sufficient level. Further, there is room for improvement in order to enhance the material strength or the transparency. Further, it is needed that a demoldability which is shown when the cured product is demolded is improved and thereby the molded body is produced with high productivity. In addition, the transparency and the demoldability are in an opposing relationship. That is, as one is improved, the other is deteriorated. Therefore, there is room for improvement in that both of the transparency and the demoldability are simultaneously improved.
Accordingly, a conventional technology has not provided the following resin composition which can be preferably used in various optical members: not only basic performances such as heat resistance but also improved optical characteristics such as transparency are exhibited; and in view of productivity, demoldability which is shown when the cured product is demolded is improved. If the molded body shows excellent characteristics and the productivity of such a molded body can be improved, the utility of the molded body as an industrial product is dramatically enhanced. Therefore, a curable resin composition for molded bodies, capable of providing such a molded body, has been needed.